Gamma-irradiated soybean meal replaced more fish meal in the diets of Japanese seabass (Lateolabrax japonicus)

A feeding trial was conducted to evaluate if gamma-irradiation or fermentation could increase the inclusion level of soybean meal (SBM) in the diet of Japanese seabass Lateolabrax japonicas. A basal diet was formulated to contain 320 g/kg fish meal. In the test diets, 25, 50 and 75% of the fish meal in the basal diet was respectively replaced by SBM in three forms (untreated, fermented or gamma-ray irradiated). Juvenile fish (13.0 ± 0.1 g) were fed with the test diets for 8 weeks. SBM treatment affected weight gain, feed intake, feed conversion ratio (FCR), phosphorus retention efficiency (PRE), phosphorus wastes output, body contents of crude protein and phosphorus, while the level of fish meal replacement affected weight gain, apparent digestibility coefficient (ADC) of protein, FCR, nitrogen retention efficiency (NRE), PRE, nitrogen wastes output (NW), condition factor, body contents of moisture and phosphorus. Weight gain, ADC of protein and NRE decreased, whereas FCR and NW increased with increasing fish meal replacement by SBM, irrespective of SBM treatments. No significant differences were found in the weight gain and NRE between fish fed the basal diet and the diets with 25% fish meal replacement by untreated or fermented SBM, or between fish fed the basal diet and the diet with 50% fish meal replacement by irradiated SBM. At the end of the feeding trial, no significant differences were found in hepatosomatic index, viscerasomatic index and proximate body composition between fish fed the basal diet and the diets with fish meal replaced by untreated, fermented or irradiated SBM. This study indicates that the use of gamma irradiation provides a novel approach to enhance the level of fish meal replacement by SBM. Fish meal in the diet for Japanese seabass can be reduced to 160 g/kg when the gamma-irradiated SBM is used as a fish meal substitute.